Gear type transfer pumps are used in many applications to pump fluids. The type of transfer pump to which this invention pertains, usually includes a pair of gears, one of which is externally driven and which in turn drives an associated gear. As is well known, the meshing and unmeshing of gear teeth between these gears effects the transfer of fluid from an inlet to an outlet.
An example of this type of fluid pump is a "gear within a gear" transfer pump. In this type of pump, an outer, driven gear (also termed "rotor") drivingly engages a smaller, internal idler gear. A crescent is usually positioned between a portion of the periphery of the idler gear and an internal periphery of the rotor. In this type of pump, the outer gear or rotor is connected to a shaft that extends axially through a housing portion sometimes termed a "backhead" and is attached directly or indirectly to a drive motor.
During operation, fluid leakage between the drive shaft and its associated housing (or backhead) is inhibited by a seal arrangement. With many prior art "gear within a gear" transfer pumps, the backhead is specifically designed to accept a certain type of seal. As an example, many prior art pumps of this type, use a "packing" type seal which includes seal material placed around the drive shaft and maintained in compression by a pressure applying member (usually a ring) that is adjustable externally of the backhead. As the packing wears, the pressure applying ring is adjusted to apply further pressure on the packing.
For applications in which packing is not suitable, the shaft housing or backhead is typically redesigned to accept the type of seal that is required for the particular application. In many if not most of these designs, maintenance and/or replacement of the seal is very difficult and time consuming.
Attempts have been made to make "cartridge seals" which are more easily replaceable. With a cartridge seal, a unitary seal assembly including rotating and non-rotating portions is installed into, or removed from the pump as a single unit. The cartridge includes structure for maintaining alignment of the various seal portions and as a result, in theory, maintenance personnel are not saddled with the task of making precise adjustments in the seal and/or are not required to carefully press fit seal portions onto the shaft or into the housing. However, it has been found that commercially available "cartridge seals" are extremely expensive and again, the shaft housing of the transfer pump must be specifically designed to accept the cartridge seal.